Passenger vehicles often include electric batteries for operating features of a vehicle's electrical and drivetrain systems. For example, in a hybrid-electric vehicle (“HEV”), a plug-in hybrid electric vehicle (“PHEV”), a fuel cell electric vehicle (“FCEV”), an extended range electric vehicle (“EREV”), or a purely electric vehicle (“EV”), an energy storage system (“ESS”) (e.g., a rechargeable ESS) may be used to power electric drivetrain components of the vehicle (e.g., electric drive motors and the like). The ESS may store high-voltage electrical energy, which may be transmitted to vehicle systems via a high-voltage (“HV”) bus having positive and negative conductors or rails. An ESS may be selectively coupled to the positive and negative conductors or rails via one or more selectively switched electric contactors. Conventional vehicle architectures utilizing ESSs, however, may not be particularly scalable in their ability to power additional vehicle systems. Moreover, conventional architectures may not allow for independent pre-charging of HV power branches.